Method for designing nonsymmetric freeform surface optical system

Abstract

The present application relates to a method for designing a nonsymmetric freeform surface optical system, and the method including the following steps establishing an initial plane system. The initial plane system is consistent with the expected system structure, but there is no focal power in the initial plane system. The image plane tilt angle of the initial plane system is defined as θ. The point-by-point method is used to calculate the coordinates and normal vectors of the data points used to construct the freeform surface. The iterative optical system is obtained by iteration; and the iterative optical system is optimized.

What is claimed is: 
     
       1. A method for designing manufacturing a nonsymmetric freeform surface optical system, comprising:
 S 10 , establishing an initial plane system comprising an image plane, wherein the initial plane system is consistent with an expected system structure, there is no focal power in the initial plane system, and an image plane tilt angle of the initial plane system is defined as θ, a process for establishing the initial plane system comprises: 
 S 11 , establishing a meridian symmetrical off-axis three-mirror system; and 
 S 12 , adjusting a decenter and a tilt of the image plane on the basis of the meridian symmetrical off-axis three-mirror system, and eliminating a light obstruction and rotating the image plane by 45° around a y-axis of a local coordinate system; 
 S 20 , calculating coordinates and normal vectors of data points of the image plane to construct a freeform surface by using a point-by-point calculating method, to obtain an iterated optical system; 
 S 30 , optimizing the iterated optical system to obtain the nonsymmetric freeform surface optical system; and 
 S 40 , making a physical element of the nonsymmetric freeform surface optical system, the physical element has a shape and is made of a material. 
 
     
     
       2. The method of  claim 1 , wherein in the step S 12 , an optical path is folded, and chief rays of a central field of view are substantially incident on a central area of the image plane. 
     
     
       3. The method of  claim 1 , wherein the step S 20  comprises:
 S 21 , defining characteristic light rays, and selecting light rays with different entrance pupil coordinates in multiple fields of view for point-by-point calculating; 
 S 22 , determining starting points and end points of the characteristic light rays; 
 S 23 , calculating coordinates and normal vectors of data points used to construct the freeform surface by using the point-by-point calculating method; and 
 S 24 , fitting a surface shape of the freeform surface according to the data points, and calculating a spatial position of the freeform surface. 
 
     
     
       4. The method of  claim 3 , wherein a full field of view design is selected when defining the characteristic light rays in the step S 21 . 
     
     
       5. The method of  claim 3 , wherein an XY polynomial is used when fitting the surface shape of the freeform surface in the step S 24 , the XY polynomial is a 6th degree XY polynomial. 
     
     
       6. The method of  claim 5 , wherein the surface shape of the freeform surface in the step S 24  is described by all terms in first N-order. 
     
     
       7. The method of  claim 3 , wherein the step S 24  further comprises transferring the coordinates and normal vectors of the data points from a global coordinate system to a local coordinate system. 
     
     
       8. The method of  claim 1 , wherein an field of view during optimizing the iterated optical system in the step S 30  is the same as a sampling field of view of the initial plane system. 
     
     
       9. The method of  claim 3 , wherein during optimizing the iterated optical system in the step S 30 , four fields of view are selected from the multiple fields of view in step S 21 , a distance between chief rays of four fields of view (4°,−3°), (4°,3°), (−4°,−3°), (−4°,3°) and chief rays of a central field of view (0°,0°) on the image plane is used as a constraint condition of an image height. 
     
     
       10. The method of  claim 1 , wherein a position of the image plane meets the requirements: a field pf view is 8°×6°, an F-number is 1.3, an effective focal length is 50 mm, an entrance pupil diameter is 38.5 mm. 
     
     
       11. The method of  claim 10 , wherein the position of the image plane further meets the requirements: a working wavelength is in a range from 8 μm to 14 μm. 
     
     
       12. The method of  claim 1 , wherein the initial plane system is completely nonsymmetric and the image plane has a β tilt angle of 45°. 
     
     
       13. The method of  claim 4 , wherein the full field of view is (0°,0°), (0°,−3°), (0°, 3°), (4°, 0°), (4°,−3°), (4°, 3°), (−4°, 0°), (−4°,−3°), or (−4°, 3°).